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Building Tips and technical articles. => 1/2 A building. => Topic started by: Andrew Tinsley on May 31, 2013, 10:56:55 AM

Title: Tank for a sheet wing profile?
Post by: Andrew Tinsley on May 31, 2013, 10:56:55 AM
I am using a modded ASP Wasp on a profile plane. I am on holiday in the US and have built a quickie to enjoy a little flying! I get stuttering on hard G corners and I am certain it is the traditional stunt wedge tank that is the culprit. Smooth stunts like loops and eights are fine. Any suggestions for a suitable tank anyone?

Andrew.

P.S. The Wasp is fitted with a Cox 0.49 TD venturi and a Texas Timers NVA assembly plus a suitable bush to hold things together.
Title: Re: Tank for a sheet wing profile?
Post by: Tim Wescott on May 31, 2013, 02:32:10 PM
I've asked almost exactly this question, and have been told to use a slack balloon tank.  They work like a charm.

Search on it here.  You want a slack balloon tank -- it'll be obvious when you see the description.

Edit:
http://stunthanger.com/smf/index.php?topic=23224.msg222337#msg222337 (http://stunthanger.com/smf/index.php?topic=23224.msg222337#msg222337)
http://stunthanger.com/smf/index.php?topic=29409.msg289587#msg289587 (http://stunthanger.com/smf/index.php?topic=29409.msg289587#msg289587)
http://stunthanger.com/smf/index.php?topic=12603.0 (http://stunthanger.com/smf/index.php?topic=12603.0)

etc.  I was hoping to find a thread with pictures, but no dice.
Title: Re: Tank for a sheet wing profile?
Post by: kenneth cook on May 31, 2013, 05:28:46 PM
       Hello Andrew, sounds to me your mod is identical to what I did. I'm glad you went that direction. I would try and cap one of the vents off and try again leaving only one open. Hopefully that solves the problem. Are you using the muffler? Muffler pressure is always an option. Later down the road when you return home, maybe trying a uniflow pipe in the tank. Maybe try and cant the rear of the tank outboard slightly. I recently ran into a problem similar using a wedge tank on a speed job. I believe the fuel load is staying on the side of the tank and not properly making it's way to the rear due to centrifugal force. The pickup may not like being all the way to the rear of the tank and may require it to be slightly off of the rear corner of the tank.

You could drill two holes about 3/32" in the center of the tank directly in the wedge and solder a smaller wedge and make a hopper from it utilizing a pickup tube in the hopper section. This way the fuel pickup is constantly submerged in fuel. Another option is to insert the wedge from the inboard side. I didn't say mount the tank on the inboard side of the fuse, but rather have it install from the inboard side projecting out the outboard side. This way you will have centrifugal force also assist in fuel feed. You can shim the tank in and out to the desired run you like. Ken
Title: Re: Tank for a sheet wing profile?
Post by: Andrew Tinsley on June 02, 2013, 07:17:37 PM
Thank you both for the suggestions. I shall be leaving for home tomorrow and will give all your suggestions a try out of interest! Ken, the Cox/TT set up is excellent. Just a pity that I only had an old Perfect tank to hand.

Regards,

Andrew.
Title: Re: Tank for a sheet wing profile?
Post by: Curare on June 04, 2013, 10:57:33 PM
Yep, slack bladders are the way to go IMO!
Title: Re: Tank for a sheet wing profile?
Post by: RknRusty on June 05, 2013, 08:58:36 PM
Since you have a Texas Timers fine thread NV, you can just use a piece of surgical tubing. TT sells it, Then use it as a pressure bladder. I use them on all of my 1/2A planes. I just make a little sack to contain the bladder and lay it on top of the wing on either side. It'll never hiccup again. Once you find your needle setting, you rarely have to fiddle with it.
The sack is secured with a string in the rear to the tail boom.
(http://i46.servimg.com/u/f46/16/76/00/59/th/lil_sa10.jpg) (http://www.servimg.com/image_preview.php?i=90&u=16760059)

It'll hold well over an ounce of fuel if you wish. Be sure and train the bladder to fill from the front before you use it the first time. For filling, I use a Luer Lock syringe with one of the fuel line plugs, also available from TT. Luer Lock syringes are cheap on the Bay. On my Tee Dee, it will really scream if you bore the venturi out to about .140", or a 9/64 drill bit will do.
Title: Re: Tank for a sheet wing profile?
Post by: Andrew Tinsley on June 07, 2013, 06:53:49 AM
Hello everyone,
I just tried a bladder and it worked, no stuttering on hard g corners. I have to admit that I don't like using them, they are ugly! however if it works it works!
Ken, I will try your suggestions to modify the hard tank and see where we get to.

Thanks everyone,

Andrew.
Title: Re: Tank for a sheet wing profile?
Post by: RknRusty on June 07, 2013, 09:35:36 AM
Excellent. Since it works so well, I'd like to ask; was it the party balloon type bladder? If so, did you make extra holes along the pickup tube, or just the one opening in the end? And how deep into the balloon did it reach?

Glad you got it working, Andrew.

Rusty
Title: Re: Tank for a sheet wing profile?
Post by: Andrew Tinsley on June 08, 2013, 07:11:48 AM
Hello Rusty,
I used a party balloon and looking at it now, it looks a bit sick! . Maybe it doesn't like nitro. I simply cut a notch in the end of the tube and position the tube end about 1/4" from the "bottom" of the balloon. I have never had problems using this set up, but I occasionally lose my nerve and put an extra notch or two in the last inch of the pipe!
 
Thanks,

Andrew.
Title: Re: Tank for a sheet wing profile?
Post by: Andrew Tinsley on June 08, 2013, 08:07:00 AM
Hello Ken,
Your uniflow suggestion, together with a slight kick out at the rear, provided a trouble free system with a clear cut off at the end of the run.
  As an aside I looked at  a C/L Big Mig 0.061. The venturi diameter was huge compared to the Cox 0.049 venturi used on the Wasp. As the engines are very comparable design wise, is the Big Mig venturi too large or the Cox venturi too small? A bit academic as both engines run well with plenty of power to spare. It is just that the disparity in throat diameter is so big.

Regards,

Andrew.
Title: Re: Tank for a sheet wing profile?
Post by: RknRusty on June 08, 2013, 08:25:53 AM
Hello Ken,
Your uniflow suggestion, together with a slight kick out at the rear, provided a trouble free system with a clear cut off at the end of the run.
  As an aside I looked at  a C/L Big Mig 0.061. The venturi diameter was huge compared to the Cox 0.049 venturi used on the Wasp. As the engines are very comparable design wise, is the Big Mig venturi too large or the Cox venturi too small? A bit academic as both engines run well with plenty of power to spare. It is just that the disparity in throat diameter is so big.

Regards,

Andrew.
I'll defer to what Ken says, but in the mean time, my guess is the Big Mig .061 venturi size reflects the larger displacement of the piston/cylinder than the .049 Tee Dee. So the .061 might pull the same vacuum through its bigger throat as the .049 pulls through the smaller one. But like you say, if they both draw fuel well, it's all academic. The Wasp might make a bit more power with the bigger venturi.